Why do subways, metro make less noise compared to traditional railways ?


Is it because they are lighter ??

In: Engineering

Yes, lighter and generally lower speeds. Metro is almost certain to be electric also, which eliminates a big source of noise compared to diesel trains. It’s also likely that “runs somewhat quietly” is a more important design requirement for metro trains than inter-city.

They are lighter per car, and shorter. Additionally, they are designed to be relatively quiet, and the routes are designed to project less sound. Much of that is because metros are usually electrically driven, which replaces the big Diesel engine. Trains are meant just to be powerful; sound is an afterthought.

For reference, each train car can vary between 30 to 130 tons depending on what’s in it, and there could be several dozen cars to a train. Subway train cars aren’t light at 38 tons, but they’re on the light end of the range, and their aren’t many of them.

Among the other good answers here, some metro designs (e.g. Montreal) use rubber tires instead of typical train wheels, and also wood brake pads saturated with some kind of oil (although I wouldn’t be surprised if the brake materials were changed with the cars that were put in use in that couple of years.

UPDATE: the brakes are soaked in peanut oil. https://youtu.be/MdvQLYC5hGc

Not sure how many systems use this design around the world though.

And anyone who has lived in the Bay Area will tell you that it’s not always the case. The old BART trains were *loud*. Not the big rumble of a freight train, but a piercing metallic screech from the wheels that you could hear for miles. New trains are slightly better with an updated wheel design.